Enhanced reductive transformation of p-chloronitrobenzene in a novel bioelectrode–UASB coupled system

The laboratory-scale upflow anaerobic sludge blanket (UASB) reactor equipped with a pair of bioelectrodes was established for the enhancement of p-chloronitrobenzene (p-ClNB) reductive transformation via the electrolysis. Results showed that a stable COD removal efficiency over 99% and high p-ClNB transformation rate of 0.328 h−1 were achieved in the bioelectrode–UASB coupled system with influent COD and p-ClNB loading rates of 2.1–4.2 kgCOD m−3 d−1 and 60 g m−3 d−1, respectively. The bioelectrodes were supplied with a voltage of 2.5–5.0 V and the effective current was above 2 mA, which resulted in a continuous supply of H2. Compared with the traditional UASB reactor (R1), the production of H2 was promoted in the bioelectrode–UASB coupled system (R2), and was consumed as an internal electron donor for p-ClNB reductive transformation by anaerobic microbes simultaneously. Furthermore, the cyclic voltammetry curve (CV) analysis of biocathodes showed a positive shift in the reductive peak potential and a dramatic increase in the reductive peak current, which demonstrated the catalytic reduction of p-ClNB by biocathode in the combined system.